Bull I need some advice on checking/calibrating temp.

[Freedom Forged]

1. Calibrated my Thermo Works thermometer with boiling water.
2. Started my RT-680 (has upgraded controller) set at 250, after it reached 250 I waited for an additional 30 minutes.
3. Placed the lead of the Thermo Works thermometer with a grate clip on the grate where I typically cook butts.
4. After closing the lid I waited 30 minutes for everything to level out.
5. Then started monitoring the thermometer.
6. The temp swings on the thermometer were wide, very wide. Anywhere from 236 at the lowest to 276 at the highest. These swing continued, there is no way for me to determine if the grill thermometer needed calibrating or not with these ridiculous swings.
7. The controller temp read out never varied more than 3 degrees. I am suspect about this.....

My reason for suspecting an incorrect temp is the amount of time it takes me to cook a 10 lb butt to an internal of 200, at a set temp of 275 is consistently 15 hours.

I would like to hear your experiences with this please.

 

[Wslayer]

Is your RT probe inside completely vertical and clean ?

 

[Freedom Forged]

Is your RT probe inside completely vertical and clean ?

Thanks for asking, I forgot to list that. Yes it is clean and vertical.

 

[Jim6820]

I think the grill controller uses an averaging algorithm to control pellet feed. The ThermoWorks is an instantaneous read, so there will always be a difference of some kind. And, temperature swings of +/- 15-20 degrees is probably pretty normal, with the average hitting pretty close to your set temperasure.

Pellet grills are not laboratory instruments, but the ThermoWorks units are much closer to that standard. I take what the RT display says as a reasonable average number and just monitor the internal temperature of the meat.

One other factor that might be contributing a little to your issue is that water boils at different temperatures at different altitudes. Not sure where you live, but calibrating a probe using boiling water can give different results, depending on the altitude. Using an ice-water bath (ThermoWorks provides a process on their web site) will produce greater accuracy.

 

[Waterboy]

As @Jim6820 said the algorithm is doing some averaging or it would go nuts trying to adjust air and pellet feed to maintain an exact temperature. To give you and idea of how good the temp control actually is do the same exercise on your oven and you’ll see major temp swings. Also make sure you use an ambient probe, not a meat probe.

 

[Freedom Forged]

As @Jim6820 said the algorithm is doing some averaging or it would go nuts trying to adjust air and pellet feed to maintain an exact temperature. To give you and idea of how good the temp control actually is do the same exercise on your oven and you’ll see major temp swings. Also make sure you use an ambient probe, not a meat probe.

The oven reference makes a lot of sense. Now that you mentioned it I did use the meat probe instead of the ambient probe.

 

[Jim6820]

Now that you mentioned it I did use the meat probe instead of the ambient probe.

I don’t think there will be any difference in temperature readings taken with ambient and meat probes (assuming they are both accurate). There are some physical differences, however. Meat probes have a sharper point to make insertion easier and they are usually longer to reach the center of larger cuts of meat. The ambient probe will have a rounded end and is usually shorter as the additional length is not needed.

What you are likely seeing is the difference between average and instantaneous readings from the RT and TW units.

 

[JGW]

Calibrate your probes with an ice bath. Unless you are at sea level, boiling water boils at different temperatures depending on your altitude. For example, where I live (at 5000+ feet), water boils at 203.

Thermoworks has both text and video on how to do an ice bath for probe/thermometer calibration. Note: 32 is 32 regardless of altitude.

Once you have a known good thermometer, you can calibrate the grill by using the temp offset (if needed).

 

[Wslayer]

The oven reference makes a lot of sense. Now that you mentioned it I did use the meat probe instead of the ambient probe.

I did check my oven once. It swung about 25° back and forth at set temp of 300°.
The ambient and meat probe won't matter. I have a meat probe set side by side with my Auber PID in my MES, they read the same.

 

[vsteel]

Mad scientist BBQ was talking to a person who helped design some controllers and he said that the variation is built in on purpose. They found they get better BBQ when things move about a little. When they made a controller that didn't move at all and was always perfect it made only so so BBQ. Now when they design a controller they on purpose put some swing into the temp to improve flavor.

 

[Freedom Forged]

Wel that is certainly interesting. Thanks